Directionality of Solar Flare Accelerated Protons and Alpha Particles from Gamma-Ray Line Measurements

Abstract

The energies and widths of gamma-ray lines emitted by ambient nuclei excited by flare-accelerated protons and alpha particles provide information on the ions directionality and spectra, and on the characteristics of the interaction region. We have measured the energies and widths of strong lines from de-excitations of 12C, 16O, and 20Ne in solar flares as a function of heliocentric angle. The line energies from all three nuclei exhibit ~1% redshifts for flares at small heliocentric angles, but are not shifted near the limb. The lines have widths of ~3% FWHM. We compare the 12C line measurements for flares at five different heliocentric angles with calculations for different interacting-particle distributions. A downward isotropic distribution (or one with a small upward component) provides a good fit to the line measurements. An angular distribution derived for particles that undergo significant pitch angle scattering by MHD turbulence in coronal magnetic loops provides comparably good fits.

References in corpus (1)

• Shape of the 4.438 MeV gamma-ray line of ^12C from proton and alpha-particle induced reactions on ^12C and ^16O

Cited by in corpus (12)

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• RHESSI as a Hard X-Ray Polarimeter
• Measurements of nuclear $\gamma$-ray line emission in interactions of protons and $\alpha$ particles with N, O, Ne and Si
• Status and Future Prospects for Gamma-Ray Polarimetry
• High resolution gamma ray spectroscopy of flares on the east and west limbs of the Sun
• Shape and Angular Distribution of the 4.438-MeV Line from Proton Inelastic Scattering off 12C
• Shape and angular distribution of the 4.438-MeV line from proton inelastic scattering off 12C
• Solar Gamma-Ray Evidence for a Distinct Population of $>$ 1 MeV Flare-Accelerated Electrons